Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 181049
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
250 AM PST Sat Nov 18 2017

.SYNOPSIS...Showers diminish tonight as a ridge of high pres builds
overhead. The ridge brings dry weather for most of the region
Saturday through early Sunday morning. A cold front crosses mainly
Sunday mid-day through mid-day Monday. Expect gusty winds, moderate
rain, and moderate Cascade snow, mainly above the passes. Next week
looks to be wet overall with rainy weather affecting at least the
first part of holiday weekend travel. Snow levels during this time
appear to remain rather high with limited impacts across the
Cascade and Coast Range passes.

&&

.SHORT TERM...Today through Monday...Radar showed scattered showers
along the coast from the vicinity of AST northward early this
morning, and may a few sprinkles still over the south WA Cascades.
Will hang on to some low pops for this morning along the south WA
coast, but otherwise a dry day today with some upper level ridging
and a weak low level offshore flow.

A shortwave moving across the broad upper ridge will push a cold
front south down the WA coast Sun. A narrow area of moist low level
isentropic lift, seen best along the 290K isentrope, will spread
increasing chances for rain into the nw part of the forecast area on
Sun. Models move the cold front se through the forecast area Sun
night and early Mon. Initially tight surface pres gradients late Sun
bring the potential for a low end high wind event Sun afternoon and
early evening for the northern part of the coast. Moisture with this
front is deep, with GFS indicating precipitable water values on the
order of 1.1 inches along the coast. The deep moisture coupled with
sw 850 mb winds on the order of 50 to 60 kt results in strong
moisture flux, meaning a period of heavy rain Sun night for much of
the region. As the front remains progressive, the area of heavy rain
will not linger for an extended period, so the potential for any
river flooding will be limited. The offshore flow ahead of the front
however will tend to keep snow levels down through Sun night, which
coupled with the heavy precipitation will likely result in some
rapid heavy snow accumulations above 4000 ft in the south WA
Cascades.

Models indicate the front has yet to clear the se corner of the
forecast area Mon morning, so will keep pops categorical there in
the morning. The upper level ridge bounces back Mon once the
shortwave is past. This likely results in the frontal boundary
stalling over sw Oregon Mon afternoon, with chances for rain
continuing over much of the the region in the lingering baroclinic
zone through the afternoon.

.LONG TERM...Monday night through Friday. Overall confidence has
improved in the forecast for next week with better model agreement.
Modesl in good agreement in lifting a warm front north through the
forecast area Mon night and Tue, so will boost pops to likely
category for most of the region. Frontal system lingers into Wed,
keeping pops high Wed. For the Thanksgiving holiday, some chance of
rain will continue across the area, but expect temperatures to be
several degrees above seasonal normals, with afternoon highs in the
mid 50s, with perhaps upper 50s at a few spots. However, snow levels
look to remain well above the Cascade passes during the time.
Another short-lived break from the rain is likely on Friday, but the
next system quickly arrives by next weekend. Cullen/

&&

.AVIATION...Clearing skies bringing spots of IFR/LIFR to the
interior valley, mainly KSLE southward. There is fog forming at
KHIO as well. Model guidance suggest fog in these areas will
clear 19-21Z. VFR should prevail at the coast today with cigs
around 3500-4500 ft lifting by midday or so. Next front
approaches tonight and affects the coast Sun with gusty south
winds 25 to 35 kt with possible gusts to 45 kt right along the
coast line.

KPDX AND APPROACHES...KPDX is clear but remains OVC047 at KTTD
which may also affect KPDX per satellite trends. Dewpoint
depression is slowly closing on saturation and if the mid level
clouds clear enough, there may be enough time for fog to develop
at KPDX for a few hours.

&&

.MARINE...Conditions will remain rather benign today as weak
high pres remains over the waters. Seas will be around 5 ft
during this time. However, a significant frontal system is
expected to arrive late night and Sun. This system looks like it
will be a period of high-end gale force southerly winds, with
some models suggesting potential for some storm force gusts.
Upgraded the Gale Watch to a Gale Warning for late tonight
through Sun evening with staggered timing for the outer and
inner zones. A low moving along the front will slow its progress
and the strong winds and seas may remain across the waters south
of Newport Sunday night. Another front is expected Tuesday for
another chance for gales.

Seas with this system will rise rapidly, peaking in
the upper teens on Sun, though the outer zones may see 20 ft for
a brief period Sun afternoon. /mh

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...High Wind Watch from Sunday afternoon through Sunday evening
     for North Oregon Coast.

WA...High Wind Watch from Sunday afternoon through Sunday evening
     for South Washington Coast.

     Winter Storm Watch from Sunday evening through late Sunday
     night for South Washington Cascades.

PZ...Gale Warning from 1 AM to 10 PM PST Sunday for Waters from Cape
     Shoalwater WA to Florence OR from 10 to 60 NM.

     Gale Warning from 10 AM to 10 PM PST Sunday for Coastal Waters
     from Cape Shoalwater WA to Florence OR out 10 NM.


&&

$$

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This discussion is for Northwest Oregon and Southwest Washington
from the Cascade crest to 60 nautical miles offshore. This area is
commonly referred to as the CWA, or forecast area.


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